She once ran a snake cult in the Tashalar and her specialty is magics that can link together spells in a sort of chain contingency spell trigger set up. Hence Elminster is wary of slaying her out of hand (and might have a tough time of it, she appears powerful) as he does not know what ramifications (in terms of blasting spells going off everywhere throughout faerun) this might have.
The Company of Crazed Venturers ran across her and ended up confronting her on a small island of the Sword Coast. To show their "power" one of the Company mages disintegrates (as per the spell) a small pebble. Shaan bends down, touches the island and disintegrates it, leaving the Company floundering in icy water while she calmly flys off.
Imprisoned in the Floating Helm of Tharados